1. Field of the Invention
The present invention relates to a plasma display panel PDP, and more particularly to a method and apparatus for driving a plasma display panel that can be driven at a low voltage and which prevents undesired discharge under a high temperature environment. Further, the present invention relates to a method and apparatus for driving a plasma display panel that is adaptive for stabilizing address operation and sustain operation.
2. Description of the Related Art
A plasma display panel displays a picture by using ultraviolet rays to cause phosphorus to emit light, with the ultraviolet rays being generated when producing discharge in an inert mixed gas such as He+Xe, Ne+Xe, He+Xe+Ne. Such a PDP is not only easily made into a thin film and a large-scale unit, but also has improved picture quality owing to recent technology development.
Referring to FIG. 1, discharge cells of a three-electrode AC surface discharge PDP in the related art includes scan electrodes Y1 to Yn, sustain electrodes Z, and address electrodes X1 to Xm crossing the scan electrodes Y1 to Yn and the sustain electrodes Z.
Cells 1 are formed displaying any one of red, green and blue at each intersection of the scan electrodes Y1 to Yn, the sustain electrodes Z and the address electrodes X1 to Xm. The scan electrodes Y1 to Yn and the sustain electrodes Z are formed on an upper substrate (not shown), and a dielectric layer and a MgO passivation layer (not shown) are deposited on the upper substrate. The address electrodes X1 to Xm are formed on a lower substrate (not shown), with barrier ribs for preventing optical, electrical crosstalk being formed between horizontally adjacent cells on the lower substrate. Phosphorus is deposited on the surface of the barrier ribs and the lower substrate and the phosphorus is excited by vacuum ultraviolet rays to emit visible light. Inert mixed gas such as He+Xe, Ne+Xe, He+Xe+Ne is injected into a discharge space between the upper substrate and the lower substrate.
In order to realize the gray levels of a picture, the PDP is driven on a time-division basis where one frame is divided into several sub-fields, each of which has a different light-emission weight. Each sub-field is divided again into an initialization period (reset period) for initializing a full screen, an address period for selecting scan lines and cells in the scan lines, and a sustain period for realizing gray levels in accordance with the number of discharge. For instance, when a picture with 256 gray levels is to be displayed, a frame period (16.67 ms) corresponding to 1/60 second is divided into eight sub-fields SF1 to SF8 as shown in FIG. 2. Each of the eight sub-fields SF1 to SF8 is divided into the initialization period, the address period and the sustain period, as described above. The initialization period and the address period of each sub-field are the same for each sub-field, while the sustain period increases at the rate of 2n (n=0, 1, 2, 3, 4, 5, 6, 7) in each sub-field.
FIG. 3 illustrates a driving waveform of a PDP, which is applied to two sub-fields.
Referring to FIG. 3, the PDP is driven by being divided into an initialization period to initialize a full screen, an address period to select cells and a sustain period to sustain discharges of the selected cells.
In the initialization period, rising ramp waveforms, Ramp-up, are simultaneously applied to all scan electrodes Y for a setup period SU. At the same time, 0V is applied to the sustain electrodes Z and the address electrodes X. Each rising ramp waveform, Ramp-up, causes a dark discharge to occur between the scan electrodes Y and the address electrodes X, and between the scan electrodes Y and the sustain electrodes Z within the cells of the full screen, with occurrence of the dark discharge generating almost no light. The setup discharge causes positive (+) wall charges to be accumulated on the address electrodes X and the sustain electrodes Z, and negative (−) wall charges to be accumulated on the scan electrodes Y. Herein, the amount of the negative (−) wall charges accumulated on the scan electrodes Y is the same as the total amount of the positive (+) wall charges accumulated on the address electrodes X and the sustain electrodes Z.
Each falling ramp waveform, Ramp-dn, is simultaneously applied to each scan electrode Y for a set-down period SD after application of each rising ramp waveform, Ramp-up. Herein, the falling ramp waveform, Ramp-dn, begins to fall from a positive voltage lower than a peak voltage of each rising ramp waveform, Ramp-up, to a ground voltage GND or a specific negative voltage level. At the same time, each sustain electrode Z is supplied with a positive sustain voltage Vs, and each address electrode X is supplied with 0V. When the falling ramp waveform, Ramp-dn, is applied, the dark discharge occurs between the scan electrode Y and the sustain electrode Z. Further, between the scan electrode Y and the address electrode Z no discharge occurs while the falling ramp waveform, Ramp-dn, drops, but the dark discharge occurs at the lower limit of the falling ramp waveform, Ramp-dn. The discharge occurring for such a set-down period SD serves to eliminate excessive wall charges unnecessary for the address discharge out of the wall charges generated for the setup period SU. When observing the change of wall charges in the setup period SU and the set-down period SD, there is almost no change in the wall charges of the address electrode X and there is a decrease in the negative (−) wall charges of the scan electrode Y. On the other hand, the polarity of the wall charges of the sustain electrode Z is positive during the setup period, but is inverted to negative during the set-down period SD because the negative wall charges are accumulated on the sustain electrode Z as much as the negative wall charges of the scan electrode Y are decreased.
In the address period negative scan pulses SCAN are sequentially applied to the scan electrodes Y and, at the same time, positive data pulses DATA synchronized with the scan pulses SCAN are applied to the address electrodes X. The wall voltage generated during the initialization period is added to the voltage difference between the scan pulses SCAN and the data pulses DATA, so as to generate address discharges within the cells to which the data pulses DATA are applied. Wall charges are formed with as much discharge as can be generated when the sustain voltages Vs are applied to the cells selected by the address discharges.
A positive DC voltage Zdc is applied to each sustain electrode Z for the set-down period and the address period, so as to reduce the voltage difference between the scan electrode Y and the sustain electrode Z, thereby preventing undesired discharge from occurring.
In the sustain period, sustain pulses SUS are alternately applied to the scan electrodes Y and the sustain electrodes Z. In the cells selected by the address discharges, sustain discharges, i.e., display discharges, occur between the scan electrodes Y and the sustain electrodes Z whenever each sustain pulse SUS is applied as the wall voltage within the cell is added to the sustain pulse SUS.
After the completion of the sustain discharge, a ramp waveform, RAMP-ERS, with narrow pulse width and low voltage level is applied to the sustain electrode Z, thereby erasing the wall charges remaining behind within the cells of the full screen.
In the related art PDP, It is not possible to prevent the voltage level of the voltages Vd, Vscan applied from the outside upon the address discharge from increasing because of the small amount of remaining wall charges on the scan electrode Y after being decreased by the discharge during the set-down period SD. Further, in the related art PDP, increase in the voltage of the sustain pulse SUS, i.e., the sustain voltage Vs, applied from the outside during the sustain period also cannot be avoided because of the small amount of wall charges accumulated on the sustain electrode Z upon the discharge during the set-down period SD. Furthermore, the related art PDP has a problem in that undesired discharges frequently occur upon the address discharge because the wall charges within the cells are decreased and their operational conditions are changed in the high temperature environment.
Further, the related art PDP has a problem in that the address operation and the sustain operation is unstable because the undesired discharge may be generated in accordance with the initial state of the off cell upon the address discharge or the sustain discharge.